In addition to the basic function of controlling opening and closing a car window, a power car window lift controller should also have a function of safety protection control, which is divided into anti-pinch control and overload control.
The anti-pinch control relates to personal safety, and has been a difficulty of safety control. A driver or passenger (especially a child) often gets hurt from being pinched by a power car window without the anti-pinch function when he/she carelessly stretches his/her head or hand out of the car window while it is closed. A MCU plus a dedicated(special) chip plus a memory chip plus various sensors is currently widely adopted at home and abroad to realize the anti-pinch control. Still some international companies adopt CAN bus and LIN bus technologies, while some Taiwan companies a method of a dedicated chip+sensors.
The overload control means that a driving motor will be overload when the car window is opened or closed in place, i.e. arrives at the bottom or upper dead center, or when a mechanical block appears during the car window is opened or closed. The controller should be switch off the motor in time, so as to prevent the motor damaging due to overload. A bimetallic strip or a PTC thermistor serially connected in the armature loop of the motor is currently widely adopted at home and abroad. Its work principle is as below: When the motor armature is locked, the current attains the highest, and the armature winding and the bimetallic strip or the PTC thermistor are heated up quickly because of overcurrent. When the temperature attains a certain value, the bimetallic strip or the thermistor turn off, thus the armature current being cut off and the motor protected. The advantage of doing so is a low cost. Its weaknesses are that an overcurrent protection element responds too slowly, and the armature winding is prolongably overloaded, which make the insulation tend to age and the service life shortened. Particularly, if a window control switch is not released, the motor will be started again after the overcurrent protection element is cooled and reset. Then the motor will be started-locked-switched off periodically. During this process, the lift mechanism, the control switch and the armature winding endure an intensive overcurrent shock, which will surely shorten the service life and lower reliability of the power car window lift. Meanwhile, the bimetallic strip and the thermistor will be out of order because of the prolonged overcurrent.